Updated | Babies with three parents could be born in the United Kingdom soon, now that regulators have given doctors at a Newcastle clinic permission. The babies are still conceived from two parents, but genetic material from one woman is inserted into another's egg to prevent the child from being born with an inherited disease.

Two women who are likely to pass a rare genetic condition on to their children will be the first to receive the treatment, The Guardian reported. Though the women aren’t identified, information in documents from British regulators indicated that both women suffered from an inherited condition called myoclonic epilepsy with ragged red fibers (MERRF).

Nearly a year ago, the clinic received a license from Britain’s Human Fertilisation and Embryology Authority to do the procedure.

Whatever children are conceived at the clinic won’t be the first to be born with three genetic parents. The first child born using this particular method is about to celebrate his second birthday. He was reportedly born in Mexico in April 2016; a researcher at a clinic in New York supervised the procedure. The Food and Drug Administration warned the doctor, John Zhang, to stop promoting the technique in August 2017, according to the Associated Press.

Before this method was developed, some people were born after something called a “cytoplasmic transfer,” also intended to treat mitochondrial genetic disorders. However, the method is quite different; rather than transferring the nucleus of a cell, only a small amount of the cytoplasm of an egg from a third person with genetically normal mitochondria is injected. As the BBC noted in 2014 , 50 people in the world may have been conceived using this method. The approach hasn’t been used in the United States since 2002.

As Nature described in April, an embryo with genetic information from three parents is created when an egg is modified to replace mitochondria—structures in the cell responsible for providing energy in a form the cell can use.

MERRF happens when certain genes in the mitochondria are mutated, according to the National Institutes of Health. Because mitochondrial DNA is passed down only from a mother to her child, replacing the mitochondria in a woman's egg with donor material from a woman without the mutation eliminates the risk. There is no cure for the condition.

This article has been updated to include more background on other fertility techniques that used a third person's genetic material.

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